Signaling system



March 7, 1944. s. E. ATKINS 2,343,515

SIGNALING SYSTEM Filed Dec. 22, 1942 lA/l/ENTOR G. E. ATKINS A rrok/vivPatented Mar. 7, 1944 SIGNALING SYSTEM George E. Atkins, Glen Ridge, N.J., assignor to 'Bell Telephone Laboratories, Incorporated, New York, N.Y., a corporation of New York Application December 22, 1942, Serial No.469,788

8 Claims.

This invention relates to telephone signaling systems and particularlyto telephone systems of the intercommunicating type.

Telephone signaling systems have been devised heretofore in which acommon talking channel provides the medium over which speech signals aretransmitted between the stations, and each station is provided with anindividual twowire signaling channel over which call signals betweenstations are transmitted and by means of which each station of thesystem may be selectively signaled. In order to reduce to a minimum thenumber of conductors interconnecting the several stations of suchsystems it has been proposed heretofore to provide fewer signalingconductors than there are stations, and to provide means for selectivelycombining each signal conductor with every other signal conductor toprovide the required number of twowire signaling channels. In accordancewith the well-known formula having to do with the number of combinationsthat are available from a predetermined number of elements taken two ata time, it is possible to effect six separate twowire channels from fourconductors; channels from six conductors; etc.

Signaling systems of the type described above require a signal device ateach station connected across the particular combination of two conductors which define the signal channel which is individual to theparticular station. Such signaling devices operate in a well-knownmanner when a signaling voltage is impressed on the correspondingchannels. However, such systems are characterized by the fact that notonly is the signal associated with a selected channel subjected to theimpressed signaling voltage but also two or more signaling devices atstations other than the selected station will be subjected, in somedegree, to the impressed voltage and will respond falsely. Thischaracteristic results from the fact that when a particular signalingchannel is selected, it is possible to trace series circuits through twoor more signaling devices between any two conductors which are combinedto effect a single signal channel.

It is the object of this invention to preclude the possibility of falsesignaling in a signaling system in which the stations of the system areinterconnected by signal conductors fewer in number than there arestations, and in which each signal conductor may be combined with everyother signal conductor to provide a separate two-wire signal channel foreach station of the system.

This object is attained in accordance with a feature of the invention byutilizing as the signal device at each station of the system'a normallyopen-circuited voltage responsive device in the nature of a cold cathodegas-filled tube, and a signaling voltage whose magnitude is such as tobe ineffective to operate such devices when connected, two or more, inseries across the signal channel to which the signaling voltage isapplied.

The invention will be readily understood from the following detaileddescription made with reference to the accompanying drawing whichdiagrammatically illustratesa six-station intercommunicating system ofthe type described above, the stations of which are interconnected bybut four signaling conductors whichmay be selectively combined in amanner to provide six separate signaling channels.

The equipment at all four stations is identical and comprises atelephone set of any well-known type, a source of current in the natureof a battery, a pair of individually operable switches for selectivelycombining the four signaling conductors to efiect six signalingchannels, a three- .element coldcathode gas-filled tube and a thermaldevicefor resetting the tube.

It is believed that the invention will be best understood from adetailed description of the operation of the system and for this purposeit will be assumed that the party at station H. de-

sires to communicate with the party at station 2 3. The subscriber atstation 12 actuates switch arm II! to contact l9 and the switch arm tocontact i and then removes the receiver, or handset from its mounting.The subscribers telephone instruments are, not'illustrated but it isintended that when the receiver or handset is removed from its mountingat any station the switchhook contacts are operated in the wellknownmanner. The switchhood contacts are illustrated in the drawing in theirnormal unactuated positions.

When the switches Ill and H are set as described and the receiver orhandset at station [2 .is removed from its mounting a circuit iscompleted' which extends from the positive terminal of battery5,switchhook contact 6 (now closed), switch I I, contact I, signalconductor 4, conductors 8 and 9 at station 24, across the control gap ofthe cold cathode gas-filled tube It, conductors I? and 13, signalconductor 2, switch contact l9, switch arm Iii, switchhook contact 20 atstation l2 to the negative terminal of battery 5. The voltage of battery5 is of sufficient magnitude to cause the tube l6 at station 24 to fire.The tube I6 fires and completes its anode circuit which includes theoperating winding of thermal device 22, normal switchhook contact 25 andbattery 26. The tube I5 accordingly functions as a visual signal whichoperates intermittently as a call signal. The thermal device 22 may beof any suitable design and functions as a self-interrupting controller.The tube I6 will continue to operate as long as the battery 5 isconnected to the signaling channel 2-4 or until the subscriber atstation 24 answers the call by removing the receiver, or handset thereatfrom its mounting. The latter act opens the anode circuit to the tube ISand the tube is extinguished. Should the station 24 be unoccupied at thetime when the call signal I6 operates, this signal device will beextinguished when the calling party at station I2 abandons the call byrestoring the receiver or handset to its mounting. When this is done,the tube IE will not refire after the last opening of its anode circuitby the device 22 since the start ing potential furnished by battery 5 isno longer connected across its control electrodes.

If the station 24 is occupied when signal device I 6 operates, the callwill be answered by the subscriber thereat in the usual manner. Whenthis is done the telephone at station 24 is connected to the commontalking channel L and conversation between the parties at the twostations I2 and 24 may be carried on, it being understood that theremoval of the receiver or handset at station I2 connects the telephoneset thereat to the line L. Talking battery, it required, may be suppliedto the common talking channel L in any suitable manner. At thetermination of conversation both parties restore their respectivereceiver, or handset to its mounting and the circuit is restored tonormal condition.

In the connection just described the signaling voltage was impressed onthe signaling channel made up of conductors 2 and 4, this signalingchannel being individual to the station 24. It will be observed,however, that a circuit may be traced from the signal conductor 2,conductors 28 and 29, control gap of tube 30 at station 23, conductors3I and 32, signal conductor 3, conductors 31 and 38, control gap of tube39 at station 34, conductors 40 and H and back to signal conductor 4.Thus when battery 5 was connected across the signal conductors 2 and 4in signaling the station 24, the voltage of this battery is alsoimpressed on th circuit just traced which inc d e Co t o ps of tubes 30and 39 at stations 23 and 34, respectively, in series, so that thesetubes are also subjected to the voltage applied to the signal channel2-4 which is individual to station 24. In systems of the type describedand which employ the usual type of signal device, such as anelectromagnetic ringer, or filament type lamp, such signal devices wouldrespond to the impressed voltage and falsely signal the stations 23 and34. By using a normally open-circuited signal device, such as the coldcathode gas-filled tube, the possibility of false signaling isprecluded. The voltage of the signal batteries at each of the stationsof the system disclosed is such as to cause the breakdown of but onetube and is insuflicient to cause two or more serially connected tubes,such as the tubes 30 and 39, to fire. Thus, when the signaling voltageis impressed on a signal channel such as the channel made up ofconductors 2 and 4 only tube I8 will be operated to bring in a callsignal at the station 24, and the signal devices 30 and 39. thoughserially connected across the channe 4.

will not operate. False signaling, accordingly, is prevented.

It is deemed unnecessary to describe in detail how each of the remainingstations of the system disclosed may be signaled from any other stationsince the description of the operation of the system hereinbefore madein connection with the origination of a call at station I2 and intendedfor station 24 sets forth all the necessary switching operationsrequired of any station subscriber in initiating a call. Suffice it tosay that station I2 is individual to the signal channel made up ofconductors I and 2; station I3 is individual to the signal channel madeup of conductors I and 3; station I4 is individual to the signal channelmade up of conductors I and 4; station 23 is individual to the signalchannel effected by combining conductors 2 and 3; and station 34 isindividual to the signal channel made up of conductors 3 and 4. Station24, as hereinbefore described, is individual to the signal channeleffected by combining conductors 2 and 4. These stations are signaledfrom a calling station by placing the signal switches at the callingstation on switch contacts associated with the signal channel individualto the desired called station in the manner described in connection withthe signaling of station 24 from station I2. It is understood, also,that the number of stations is not limited to the six stationsillustrated. Any desired number of stations may be accommodated in thesystem disclosed.

Though the invention is shown applied to a telephone signaling system itis apparent that it is suitable for use in other applications of remoteselective control wherein it is desirable to selectively control theoperation of a number of devices over a signal conductors fewer innumber than the number of devices.

It is also understood that systems incorporating this invention need notbe limited to a common talking circuit. If the impedance of theconductors is kept sufiiciently low to preclude cross talk twoconversations may be carried on simultaneously over three wires, andaccordingly the signaling combinations may be used as speech channels.

What is claimed is:

l. The combination in a signaling system of a plurality of stations, aplurality of signal conductors fewer in number than the number ofstations, a signaling channel for each station comprising a differenttwo-wire combination of said signal conductors, certain of said two-wirecombinations including a common one of said signal conductors, anormally open-circuited signaling device terminating each of saidsignaling channels, a source of signaling voltage at each of saidstations, and means at each of said stations for selectively connectingits respective source of signaling voltage to said signaling channels.

2. The combination in a signaling system of a plurality of stations, aplurality of signal conductors fewer in number than the number ofstations extending between said stations, means at each of said stationsfor selectively combining each of said signal conductors with everyother signal conductor to effect a plurality of distinct twowiresignaling channels greater in number than the number of signalconductors, and a normally open-circuited signal device connected acrosseach of said signaling channels.

3. The combination in a signaling system of a plurality of stations,signal conductors fewer in number than the number of said stationsinterconnecting said stations, switches at a station for selectivelycombining each of said signal conductors with every other signalconductor to effeet a plurality of distinct two-wire signaling channelsgreater in number than the number of signal conductors, a normallyopemcircuited signal device at each of said stations permanentlyconnected across a different two-wire signaling channel, and means at astation for impressing a signaling voltage on the two-wire signalingchannel efiected by the operation of said switches.

4. The combination in a signaling system of a plurality of stations, aplurality of signal conductors fewer in number than the number ofstations extending between said stations, selectively operable means ateach station for combining each of said signal conductors with everyother signal conductor to eflfect a plurality of distinct two-wiresignaling channels greater in number than the number of signalconductors, and a space discharge signal device connected across each ofsaid signaling channels.

5. The combination in a signaling system of a plurality of stations, aspace discharge signal device at each of said stations, a source ofvoltage at a station for initiating the operation of said signaldevices, and means at a station for selectively connecting said sourceof voltage to the control electrodes of each of said signal devices,said connecting means comprising signal conductors fewer in number thanthe number of said stations and associated with the control electrodesof said signal devices and means for connecting said source of voltageto said signal conductors selectively in pairs.

6. The combination in a signaling system of a plurality of stations, aplurality of signal conductors fewer in number than the number ofstations extending between all of said stations, a normallyopen-circuited signal device at each station responsive to apredetermined value of voltage and so connected to said signalconductors that when a particular pair of said signal conductors iscombined to efiect a two-wire signal channel a signal device at one ofsaid stations is connected directly across the efiected signal channeland the signaling devices of at least two other of said stations areconnected in normally open-circuited space discharge signal device ateach of said stations, each signal device having its terminals connectedacross a different signaling channel made up of various two-wirecombinations of said signal conductors, means at each of said stationsfor seizing said signal conductors in various combinations of twoconductors to selectively establish conections to the said signalingchannels, and means at said stations for impressing a signaling voltageon the selected two-wire combinations of said signal conductors toselectively operate the space discharge signal devices associated withthe corresponding signaling channels.

8. The combination in a telephone signaling system of a multistationline circuit, signal conductors of lesser number than the number ofstations on said line, a space discharge signal de vice at each stationhaving a pair of control electrodes, means permanently connecting oneelectrode of each of a group of said signal devices to a common one ofsaid signal conductors, means permanently connecting the other electrodeof each of said group of signal devices to separate others of saidsignal conductors, means at a station for selectively combining the saidcommon one of said signal conductors with each of the said others ofsaid signal conductors, and means at a station for impressing asignaling voltage on a selectively combined pair of said signalconductors to cause the operation of the signal device whose electrodesare connected to the selected signal conductors.

GEORGE E. ATKINS.

